The original PlayStation 4 will be replaced by this newer, slimmer PS4.
By the end of September, this newer, smaller model will be on store shelves. Internally, it's not especially different from the regular PS4. It will run the same games in the exact same ways as before.
Externally, it's much less bulky than its older brother. It inexplicably retains the shape of the original, but it will not take up nearly as much space underneath your TV as before.
The base model of the slim PS4 will retail for $299 with a 500gb hard drive, both the same as the original console. This will phase out the old PS4 over time.
If you don't already have a PS4 and you want one this year, there's another option: the PS4 Pro.
The PS4 Pro comes out on November 10 for $399. It looks like if you stacked the other two consoles on top of each other for a reason: It's got more processing power under the hood.
The PS4 Pro is meant for people riding the bleeding edge of technology. The extra horsepower allows it to display games in ultra-sharp 4K resolution with high-dynamic range (HDR) on newer TVs that support those features.
If you still have a regular old 1080p TV, there are still reasons to get this one. With the extra processing power, games can look and perform better than before. Note that this mostly applies to upcoming games, with some older games (such as "Infamous: First Light") being grandfathered in.
If you already have a PS4, there doesn't seem to be any reason to upgrade right now. If you don't have one yet and you want the best console gaming experience on your nice TV, this is the way to go right now.